OK, some rules/guidelines...
- As ridiculous as the plot gets, we don't let it degenerate into something that's just a complete mess. It's about taking a story thread (or introducing a new one) and doing something with it. You can take it in a completely new direction, but don't run it into the ground. This includes things like gratuitously killing off characters, introducing too many new characters too fast or throwing in cheap revelations/plot twists that serve no purpose or just aren't credible within the story. This is obviously going to depend on personal judgement to a large extent. You can be as silly as you like, just don't kill the thing.
- If you decide to join in, your scene or scenes have to be substantial. They don't have to be long, but they do have to take the plot thread you've chosen to continue somewhere. Cliffhangers are fine, but try not to use any that will overly restrict what the next person can do. And no leaving final sentences incomplete for others to finish. You finish your scenes.
- Although this is fundamentally a boardfic, the 'movie' should stand on its own as something that would be enjoyable for someone who doesn't know us (newbies, for example). Board in-jokes and Pratchett references are fine as long as the scene still works independently of knowledge of specific books or running board gags and they don't obscure the plot. Otherwise we'll end up with the kind of thing highlighted in the first point.
That's about it, as far as I can see for now. If anything else becomes problematic or emerges later on, we can add new guidelines if we need to.